The Third Generation Project Partnership (3GPP) has developed the System Architecture Evolution (SAE) as the core network architecture of its future and Long Term Evolution (LTE) wireless mobile telecommunications standard. The main component of the SAE architecture is the Evolved Packet Core (EPC; see “Architecture enhancements for non-3GPP Accesses,” 3GPP TS 23.402). The LTE/SAE network includes network entities supporting the user and control planes.
An ongoing trend within telecommunications is the convergence of fixed and mobile networks, which is known as Fixed Mobile Convergence (FMC). The trend of evolving networks using IP-based technologies is common for fixed and mobile networks, which makes the convergence easier. Through FMC, mobile and fixed network operators will be able to utilize their network resource more efficiently, which leads to reduction of capital and operational expenditure (CAPEX and OPEX). For instance, when a user is running an IP-based application such as Multimedia Telephony (MMTel) inside their home, it is more efficient to utilize broadband connectivity of the fixed access network rather than the wireless access network.
Residential networks have been important to the success of FMC because they are the most commonly used fixed network access by ordinary users. Therefore, it is important to be able to connect mobile phones to the Evolved Packet Core (EPC) through a residential network. The term User Equipment (UE) is used interchangeably herein in place of the term mobile terminal or mobile phone, or even just terminal or device. The term UE is familiar in the 3rd Generation Partnership Project (3GPP) documentation, and is intended to refer to any piece of equipment that is configured to access the internet; it would include, for example and without limitation, mobile telecommunication devices, portable or handheld computing devices and desktop or installed computers. However, for the purposes of this disclosure and the inventive techniques described herein, the term is not necessarily limited to devices that support 3GPP standards.
3GPP defines mobile 2G/3G/LTE accesses and “non-3GPP accesses” (TS 23.402). The latter can be a fixed network. The BBF (BroadBand Forum, the standardization organization for the fixed access; see http://www.broadband-forum.org/) defines an architecture for fixed networks. There is an ongoing joint work item on FMC between these two organizations [3GPP TR 23.839, now moving into TS 23.139, and BBF WT 203]. Many UEs address the FMC trend by providing multiple radio interfaces: one interface to connect to a 2G/3G/LTE access and a WiFi interface to connect to a fixed network.
There are a number of ongoing work items on Fixed Mobile Convergence (FMC). In FMC, a dual-radio UE is generally assumed. The UE has one radio interface for the 3GPP access (e.g. LTE), and one radio interface for the fixed access (e.g. WiFi). In 3GPP, “Study on Support of BBF Access Interworking” (BBAI) covers interworking between 3GPP (the standardization organization for mobile networks) and BBF (the standardization organization for fixed networks) [3GPP TR 23.839, TS 23.139, BBF WT 203].
Additional standardization activities are ongoing in the WiFi Alliance. In the WiFi Alliance, one of the focus areas is (public) hotspots. Therefore, in addition to the residential networks described above, hotspots are increasingly becoming key to the success of FMC, and there is a work item in 3GPP called SaMOG (Study on S2a mobility based on GTP & WLAN access to EPC; see 3GPP TR 23.852 at http://www.3gpp.org/ftp/Specs/html-info/23852.htm). SaMOG is specific to S2a, but not specific to BBF.
A 3GPP UE can attach to a non-3GPP access network and connect to one or more Packet Data Networks (PDNs) via the S2 interface [3GPP TS 23.402]. The S2 interface comes in three types: S2a, S2b and S2c. The latter two overlay the non-3GPP access network and do not impact it. S2a is a more converged solution that does impact nodes in the non-3GPP access network. In S2a, the non-3GPP access network is seen as trusted; the non-3GPP access network is therefore denoted as TNAN (Trusted Non-3GPP Access Network). Where the TNAN uses Wireless LAN (WLAN) as the radio technology towards the UEs, the TNAN is denoted as TWAN (Trusted WLAN Access Network). S2a over TWAN is now standardized in 3GPP [Chapter 16 of 3GPP TS 23.402].
FIG. 1 of the accompanying drawings is a schematic block diagram providing an architecture overview, illustrating a UE 2 connecting to a 3GPP domain 4 via a TNAN 6. The TNAN 6 comprises a Residential Gateway (RG) 8, an Access Node 10 and a gateway node denoted as a TNAN S2a Peer (TNSP) 12. The 3GPP domain 4 comprises one or more PDN Gateways (PGWs) 14. In a case where the TNAN is a TWAN 6, the gateway node in the TWAN 6 is denoted as a TWAN Access Gateway (TWAG) 12.
In S2a, there is a GPRS Tunnelling Protocol (GTP) or Proxy Mobile IP (PMIP) tunnel for each PDN connection between the TNSP or TWAG 12 (e.g. a BBF Border Network Gateway (BNG)) in the TNAN or TWAN 6 and the 3GPP PGW(s) 14. Each PDN connection is anchored in a 3GPP PGW 14. The UE receives one IP address for each PDN connection, and it is the PGW that assigns the address. Similarly, between the UE 2 and the TNSP or TWAG 12 a point-to-point link is provided in order to separate the traffic from the different UEs and PDN connections.
A point-to-point link can be considered to be a protocol that provides a logical direct connection between two networking nodes. A data frame sent from node A via a point-to-point link to node B will not pass a node C. Note that a “point-to-point link” is a logical concept and can be implemented in several ways. The network between the UE 2 and the TNSP or TWAG 12 would generally be Ethernet based. Nodes intermediate the UE 2 and the TNSP 12 do forced-forwarding towards the TNSP 12 on L2 (Ethernet). The TNSP 12 sends downstream traffic targeted for the UE 2 as unicast on L2, even if that traffic is multicast/broadcast on L3 (IP).
Such an implementation imposes a limited impact on the UE 2 and the existing TNAN or TWAN infrastructure (in particular when TNAN or TWAN is defined by BBF). More importantly, there is no impact on the UE 2 if the UE 2 only has one default PDN connection. The TNSP or TWAG 12 can distinguish the different PDN connections based on UE MAC (Media Access Control) address combined with the PDN connection IP address that was assigned to the UE 2.
There are other ways to implement a point-to-point link between the UE 2 and TNSP 12. Examples are: a L3 tunnel (e.g. IPsec or IP-in-IP), a L2 tunnel (e.g. L2TP), and so on. However, all of these tend to have a greater impact on the UE 2 or the TNAN infrastructure.
The present applicant has appreciated a problem with the above-described architecture. In particular, it has been appreciated that there could be a situation where a set of one or more PGWs assign the same IP address for different PDN connections. This could occur where, for example, there are two PDNs connections relating respectively to two closed corporate networks, each with their own addressing scheme. Each PDN might be served by a different PGW, and each PGW might be managed by a different operator. The 3GPP domain(s) and the UE are designed to handle such an overlap without any issue. However, the problem is that the TNSP or TWAG will get confused; it will no longer be able to map upstream traffic to the correct GTP/PMIP tunnel.
It should be noted that the likelihood of such a problem occurring in a real deployment is small; most UEs will only use a single PDN connection, and the IP addressing schemes of different PDNs will in most cases not overlap. However, the problem can and will occur without a solution, and the present applicant has appreciated the desirability of addressing this issue.
There are typically two scenarios where such a problem of overlapping or clashing addresses when a UE access a 3GPP core network via a non-3GPP access network can arise. In both scenarios, a dual-radio UE is assumed; the UE has one radio interface for the 3GPP access (e.g. LTE), and one radio interface for the non-3GPP access (e.g. WiFi).
A first scenario is illustrated schematically in FIG. 2 of the accompanying drawings. In the first scenario, the UE 2 is initially connected to a 3GPP access 16, and already has overlapping addresses in the 3GPP access 16, or has an address in the 3GPP access 16 which overlaps with an address already assigned in the non-3GPP access 6. As mentioned previously, overlapping addresses in the 3GPP access presents no problem; 3GPP by design allows for such a situation. However, a problem occurs when the UE now does a handover to the non-3GPP access 6. This can be considered as the first scenario.
In a second scenario, the UE 2 is attached to a non-3GPP access 6 and opens a new PDN connection. The new address for that PDN connection overlaps with an existing address in the second scenario.
The present applicant has appreciated the desirability of addressing the above-identified issues, and particularly in a manner that (a) does not tend to pose restrictions on the deployment of S2a in certain circumstances; and/or (b) enables the UE to distinguish between downlink IP multicasts if these come from different PDNs.